MODE. E. W. Anderson, F. P. Hood, and Dr. F. A. Bovey find that true mode of addition of an isopropyl acrylate is trans
of stereospecificity of the methylene group in the polymer backbone is meaningless. All hydrogens of the methylene are identical. However, substitution of a deuterium atom for one of the hydrogens allows studying the stereochemical nature of the methylene, Dr. Bovey told the Symposium on New Aspects of Elastomer Stereospecific Polymerization. The symposium was held jointly by the Division of Rubber Chemistry and the Division of Polymer Chemistry during the recent 148th ACS National Meeting. The labeled methylene was studied by its effects on nuclear magnetic resonance spectra of labeled and unlabeled polymer. Labeling. Dr. C. Schuerch and his group at Syracuse prepared the labeled monomer by trans addition of deuterium to isopropyl propiolate. Polymerization was carried out in toluene at - 7 8 ° C. by Dr. W. Fowells. A Grignard reagent, phenylmagnesium bromide, initiates the anionic polymerization. For comparison, an isotactic nondeuterated polymer was made the same way from isopropyl acrylate. An atactic nondeuterated polymer was also prepared, by free radical polymerization. NMR spectra of the deuterated polymer contain singlets at 7.86 T and 8.32 T. These peaks correspond to erythrodiisotactic and threodiisotactic sequences of monomer units. In the erythrodiisotactic structure, beta hydrogens (the hydrogens originally on the double bond) are on the same side of the polymer backbone's planar zigzag as are the ester groups. In the threodiisotactic struc50
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ture, the beta hydrogens are on the opposite side. NMR data show that both the labeled and unlabeled anionically polymerized polymers are nearly 100% isotactic with respect to the ester groups. Theoretical calculation of NMR spectra was done to identify precisely the two types of beta protons observed. To calculate NMR spectra of the type represented by this polymer (where the protons experience very strong electron coupling to each other), a digital calculating machine must be used. The quantum mechanical calculations are very laborious when there are as many as six spins (six coupled nuclei) involved. This part of the study was devised by Dr. L. C. Snyder and R. L. Kornegay of Bell. Re-examine. Existing proposals concerning the mechanism of stereospecific anionic polymerization apparently require an equal degree of stereospecificity at both carbon atoms of the monomer's double bond, Dr. Bovey says. Because the methylene groups have been found to be random, he says, the mechanism must be reexamined. Dr. Bovey feels that a distinction must be made between two modes of addition to understand the mechanism. The true mode of addition is the actual direction in space along which the active chain-end and monomer approach each other. The apparent mode of addition is the direction of addition as judged by the stereochemical configuration about the resulting bond. The true mode of addition is trans, Dr. Bovey says. Steric considerations rule out cis. The configuration of the polymer chain will then depend on what happens at the growing chainend. If the mode of presentation is "isotactic-like," the beta protons in the isotactic sequences will be threo. If the mode of presentation is "syndiotactic-like," the addition takes place in an apparently cis manner although the true path is trans. For this to happen in the latter case, the planar chain-end would have to rotate; this occurs under the influence of the metal counter-ion. In the NMR work, Dr. Bovey and his co-workers observed erythro and threo methylene proton peaks of nearly equal intensity. In terms of the distinction in mode of addition, the isotactic-like and syndiotactic-like monomer presentations must be regarded as about equally probable.
Bonding in Arene Mefai Complexes Clearer Three-dimensional x-ray studies of two chromium tricarbonyl compounds completed New information has been obtained concerning the nature of bonding of arene metal complexes. Dr. Lawrence F. Dahl and Marcia F. Bailey of the University of Wisconsin have completed three-dimensional x-ray structural determinations of two chromium tricarbonyl compounds: thiophene chromium tricarbonyl and hexamethylbenzene chromium tricarbonyl. Three-dimensional, single x-ray crystal analysis of hexamethylbenzene chromium tricarbonyl, which includes anisotropic least squares refinement, shows that the methyl carbon atoms are coplanar with the benzene carbons within the limits of experimental error. Also, the C r ( C O ) 3 fragment is oriented in such a way that the other three assumed octahedral chromium orbitals are pointed toward the midpoints of the alternate C—C bonds of the hexamethylbenzene ring. This C r ( C O ) 3 configuration rules out the possibility of a twofold molecular disorder, Mrs. Bailey told the Division of Inorganic Chemistry during the 148th ACS National Meeting. The Wisconsin scientists observed no threefold distortion of the ring although an anomalous twofold distortion of both the benzene arid methyl carbons is indicated. The two shorter C—C bonds found are 1.37 A. (average) vs. the other four C—C bonds having an average length of 1.44 A. This may be attributed to the interaction of freely rotating methyl groups on a given ring and to packing effects. Mrs. Bailey says that it's important to note that no observable threefold distortion of the ring occurs. Two recent x-ray studies by others of dibenzene chromium have given conflicting results for the symmetry of the pi-bonded benzene ring. The x-ray diffraction studies by one group of scientists indicate that, within the limits of experimental error, all C—C bonds of the benzene ring are equivalent. Also, the sixfold symmetry of each benzene ring is maintained in this organochromium complex and no localization occurs in the ring when it bonds to the chromium atom. Another group, however, has found a significant difference in alternate bond lengths. This supports the as-
The business-minded administrationof Governor John J. McKeithen is injecting new vitality into industrial Louisiana, and industry is responding at an unprecedented rate. Backed by a Legislature that proved in its May-July, 1964 session that it was thoroughly in accord with the industry-oriented plans of the new administration, these acts were passed: 1. Entitling industrial users of natural gas to be granted a credit applicable to all corporate state and local taxes. This saves industry money. 2. Permittingthe establishment of special industrial districts not subject to inclusion in service taxing districts such as sewerage, water, light, street and fire protection. This act saves industry from additional taxation. 3. After the ten-year exemption from property taxes on plant and equipment granted to new industry, this act provides that the properties will be assessed at the average rate of all other property. This insures new industry of equitable long-range tax treatment.
4. Prohibiting intervention or control of industrial gas negotiations and sales by state government. This allows industry to negotiate freely for natural gas. These are the major industries that have announced new or expanded plant installations in Louisiana during the period January-June, 1964:
Corporation
Plant Investment
Borden
$ 9 million
Crown-Zellerbach
$ 29 million
Dow
$ 25 million
Ethyl
$ 10 million
Hooker
$ 35 million
Humble
$ 11 million
Kaiser
$ 7 million
Monsanto
$ 12 million
Olin Mathieson
$ 40 million
Texaco
$ 75 million
Union Carbide
$ 50 million
U. S. Rubber & Imperial Chemical
$ 20 million
Wyandotte
$ 10 million
Total
"Over a n d above t h e Acts directly designed t o m a k e Louisiana more a t t r a c t i v e a n d profitable t o indust r y , t h e Legislature passed our Code of E t h i c s bill, Centralized Purchasing, C e n t r a l Listing of all S t a t e Employees, and I n v e n t o r y of S t a t e P r o p e r t y bills. All were introduced in our t o t a l effort t o m a k e Louisiana a b e t t e r place to live, work and prosper. "Louisiana is rich a n d a b u n d a n t in n a t u r a l resources—oil, gas, salt, sulphur and lime — with m a n y companies already producing basic a n d i n t e r m e d i a t e chemicals. W e h a v e limitless fresh w a t e r for process use, a n d our w a t e r w a y s afford direct a n d inexpensive t r a n s p o r t a tion. Our labor force is unsurpassed. " T h i s is t h e beginning of a new era for Louisiana, a n d t h e real potential is yet t o be t a p p e d . W o n ' t you call or write m e in B a t o n Rouge? I assure you t h a t your inquiry will receive m y personal a t t e n t i o n / '
$333 million
This first six months investment is leading Louisiana to its greatest industrial record—and the full impact of the new industrial-inducement legislation is yet to be felt.
LOUISIANA
A special message to industrial decision-makers from the new Governor of Louisiana.
Governor of Louisiana
means Business-now!
When you have to separate under pressure, get a centrifuge that stands up.
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New Study Confirms Structure of a Chromium Tricarbonyl
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FOR WOOD FLOORS
Representation of thiophene chromium tricarbonyl, C4H4SCr(CO)3, shows the threefold crystallographic disorder of the thiophene ring. Structural analysis of this compound by the Wisconsin scientists confirms the structure proposed by others
sumption that three octahedral orbitals of the chromium atom are directed to three of the C—C bonds of each benzene. This then causes partial localization of the pi-electrons of the ring and a partial reduction of the molecular symmetry. Confirms. The structural analysis of thiophene chromium tricarbonyl confirms the structure proposed by other scientists, which suggests a threepoint attachment of both the olefmic groups and the sulfur to the C r ( C O ) 3 fragment to give octahedral coordination to the chromium. The threefold orientational disorder of the thiophene ring prevents a detailed comparison of the molecular parameters of the metal-complexed thiophene with those of free thiophene. The Wisconsin scientists have applied a rigid-body technique to the thiophene ring (in the least squares refinement of the structure) to solve the crystallographic disorder problem. The threefold disorder of the thiophene ring in the thiophene chromium tri-
carbonyl has been confirmed by them. In relation to the hexamethylbenzene chromium tricarbonyl structure, this underscores the conclusion that a twofold disorder of a chromium tricarbonyl-ring compound (to account for the lack of threefold variation in bond lengths in the hexamethylbenzene ring) is unlikely, Mrs. Bailey says. A threefold disorder in hexamethylbenzene chromium tricarbonyl would have no effect on a possible threefold distortion of the benzene ring.
Mn, Ni, Co, and U0 2 Perchlorate Complexes Made Anionic complexes of manganese ( I I ) , cobalt ( I I ) , nickel ( I I ) , and U 0 2 2 + which contain perchlorate as the only ligand have been prepared by Dr. Darel K. Straub and Ying-Mae Yung of the University of Pittsburgh. Success in preparing these compounds is based to a large degree on the use
Easy mark for heels and d i r t is the floor p o l ished with conventional paste or liquid waxes. Floor at left and right were both subjected to equal traffic.
High gloss on application without buffing plus greater slip- and scuffresistance are characteristic of wood floors polished with NeoCrylbased formulations.
NeoCryl B-700 and B-705 are free-flowing, granular acrylic copolymers that provide best-selling features (see above) to solvent-based polishes for wood floors. They produce a hard, dirt-resistant finish. Protect floors and the sealer, as well, minimizing frequency of refinishing. Selfcleaning on re-application. Stable. Easy to strip with mineral spirits. Write for new NeoCryl Technical Bulletin and state if you would like samples* SPECIALISTS IN HIGH POLYMERS
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SEPT.
21, 1964
C&EN
53
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